This invention relates generally to gun chambering and more particularly to a method for chambering a gun barrel.
A barrel for a modern small arm typically includes an integral chamber which receives and supports a cartridge casing during firing. Most commonly used cartridges are identified by a standard specification defined by a recognized commercial standards organization, for example the Sporting Arms and Ammunition Manufacturer""s Institute (xe2x80x9cSAAMIxe2x80x9d), or by a military organization such as the North Atlantic Treaty Organization (xe2x80x9cNATOxe2x80x9d). These specifications provide nominal dimensions for a cartridge. A firearm intended for a particular caliber is manufactured having chamber dimensions designed to accept the specified cartridge with clearances that ensure reliable functioning under expected operating conditions. These operating conditions may include normal manufacturing variations in the cartridge, and in the case of military arms, rapid or crude manufacturing standards or operation under adverse conditions.
In order to achieve more consistent performance, guns and ammunition may be custom-made to stricter-than-standard tolerances. For example, a competitive target shooter firing carefully hand-loaded ammunition under clean, controlled conditions may be able to use a gun with a chamber machined to a smaller-than-normal diameter in the neck area, or having an increased depth of bullet seating in the barrel rifling. Either of these changes could cause unacceptable loading and extraction problems in a gun designed for ordinary use.
In a further effort to get customized performance, xe2x80x9cwildcatxe2x80x9d cartridges have been developed. Wildcat cartridges are typically based on a standard cartridge, or a universal cartridge blank as a starting point. The cartridge cases are then xe2x80x9cfire-formedxe2x80x9d by placing them in a chamber machined to the selected wildcat caliber and firing them. The gas pressure forces the cartridge case to conform to the chamber walls.
In the case of either competitive shooting or wildcatting, it is necessary to form a custom gun chamber. Prior art chambers are formed with chambering reamers. A chambering reamer is a precision cutting tool made from tool steel or similar material. Forming a custom chamber with reamers usually requires three successive cuts, and thus three custom-made reamers. This method is expensive and time consuming. Most reamers are intended for use by hand operation, not machine driven. Furthermore, the reaming process cold-works the barrel, inducing stresses which then must be removed through heat-treatment, which adds to the extra cost of production. In addition, a chambering reamer depends for centering on a pilot which extends into the bore of the barrel, thus degrading concentricity of the chamber to the bore if metal chips are allowed to build up and gall in the pilot area. This can also result in the cutting of a new chamber that is not perfectly centered.
Accordingly, there is a need for an apparatus and method for forming custom chambered gun barrels which is accurate and economical.
The above-mentioned need is met by the present invention, which provides a method and apparatus for machining a gun barrel chambering by an EDM process. A conductive electrode is used which reproduces the desired shape and dimensions of the chamber. A series of electrodes of progressively increasing diameter may be used. Also, an electrode for an EDM barrel chambering process is provided in the form of an axisymmetrical conductive member, and may include a body with taper, an angular shoulder, a neck, a throat area, and a tapered lead angle portion into the bore along with other features of a selected cartridge chamber.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.